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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.util;

/**
 * This class provides a skeletal implementation of the <tt>Set</tt>
 * interface to minimize the effort required to implement this
 * interface. <p>
 *
 * The process of implementing a set by extending this class is identical
 * to that of implementing a Collection by extending AbstractCollection,
 * except that all of the methods and constructors in subclasses of this
 * class must obey the additional constraints imposed by the <tt>Set</tt>
 * interface (for instance, the add method must not permit addition of
 * multiple instances of an object to a set).<p>
 *
 * Note that this class does not override any of the implementations from
 * the <tt>AbstractCollection</tt> class.  It merely adds implementations
 * for <tt>equals</tt> and <tt>hashCode</tt>.<p>
 *
 * This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @param <E> the type of elements maintained by this set
 * @author Josh Bloch
 * @author Neal Gafter
 * @see Collection
 * @see AbstractCollection
 * @see Set
 * @since 1.2
 */

public abstract class AbstractSet<E> extends AbstractCollection<E> implements Set<E> {

  /**
   * Sole constructor.  (For invocation by subclass constructors, typically
   * implicit.)
   */
  protected AbstractSet() {
  }

  // Comparison and hashing

  /**
   * Compares the specified object with this set for equality.  Returns
   * <tt>true</tt> if the given object is also a set, the two sets have
   * the same size, and every member of the given set is contained in
   * this set.  This ensures that the <tt>equals</tt> method works
   * properly across different implementations of the <tt>Set</tt>
   * interface.<p>
   *
   * This implementation first checks if the specified object is this
   * set; if so it returns <tt>true</tt>.  Then, it checks if the
   * specified object is a set whose size is identical to the size of
   * this set; if not, it returns false.  If so, it returns
   * <tt>containsAll((Collection) o)</tt>.
   *
   * @param o object to be compared for equality with this set
   * @return <tt>true</tt> if the specified object is equal to this set
   */
  public boolean equals(Object o) {
    if (o == this) {
      return true;
    }

    if (!(o instanceof Set)) {
      return false;
    }
    Collection<?> c = (Collection<?>) o;
    if (c.size() != size()) {
      return false;
    }
    try {
      return containsAll(c);
    } catch (ClassCastException unused) {
      return false;
    } catch (NullPointerException unused) {
      return false;
    }
  }

  /**
   * Returns the hash code value for this set.  The hash code of a set is
   * defined to be the sum of the hash codes of the elements in the set,
   * where the hash code of a <tt>null</tt> element is defined to be zero.
   * This ensures that <tt>s1.equals(s2)</tt> implies that
   * <tt>s1.hashCode()==s2.hashCode()</tt> for any two sets <tt>s1</tt>
   * and <tt>s2</tt>, as required by the general contract of
   * {@link Object#hashCode}.
   *
   * <p>This implementation iterates over the set, calling the
   * <tt>hashCode</tt> method on each element in the set, and adding up
   * the results.
   *
   * @return the hash code value for this set
   * @see Object#equals(Object)
   * @see Set#equals(Object)
   */
  public int hashCode() {
    int h = 0;
    Iterator<E> i = iterator();
    while (i.hasNext()) {
      E obj = i.next();
      if (obj != null) {
        h += obj.hashCode();
      }
    }
    return h;
  }

  /**
   * Removes from this set all of its elements that are contained in the
   * specified collection (optional operation).  If the specified
   * collection is also a set, this operation effectively modifies this
   * set so that its value is the <i>asymmetric set difference</i> of
   * the two sets.
   *
   * <p>This implementation determines which is the smaller of this set
   * and the specified collection, by invoking the <tt>size</tt>
   * method on each.  If this set has fewer elements, then the
   * implementation iterates over this set, checking each element
   * returned by the iterator in turn to see if it is contained in
   * the specified collection.  If it is so contained, it is removed
   * from this set with the iterator's <tt>remove</tt> method.  If
   * the specified collection has fewer elements, then the
   * implementation iterates over the specified collection, removing
   * from this set each element returned by the iterator, using this
   * set's <tt>remove</tt> method.
   *
   * <p>Note that this implementation will throw an
   * <tt>UnsupportedOperationException</tt> if the iterator returned by the
   * <tt>iterator</tt> method does not implement the <tt>remove</tt> method.
   *
   * @param c collection containing elements to be removed from this set
   * @return <tt>true</tt> if this set changed as a result of the call
   * @throws UnsupportedOperationException if the <tt>removeAll</tt> operation is not supported by
   * this set
   * @throws ClassCastException if the class of an element of this set is incompatible with the
   * specified collection (<a href="Collection.html#optional-restrictions">optional</a>)
   * @throws NullPointerException if this set contains a null element and the specified collection
   * does not permit null elements (<a href="Collection.html#optional-restrictions">optional</a>),
   * or if the specified collection is null
   * @see #remove(Object)
   * @see #contains(Object)
   */
  public boolean removeAll(Collection<?> c) {
    Objects.requireNonNull(c);
    boolean modified = false;

    if (size() > c.size()) {
      for (Iterator<?> i = c.iterator(); i.hasNext(); ) {
        modified |= remove(i.next());
      }
    } else {
      for (Iterator<?> i = iterator(); i.hasNext(); ) {
        if (c.contains(i.next())) {
          i.remove();
          modified = true;
        }
      }
    }
    return modified;
  }

}
